1. Field of the Invention
This invention relates to control device for hybrid vehicle, having an engine and an electric motor, and, more particularly, to a control device for hybrid vehicle for effectuating switching between a motor running mode and an engine running mode.
2. Description of the Related Art
A control device for a hybrid vehicle has heretofore been well known as including an engine and electric motor that enable the switching between a motor running mode relaying on a drive-power source composed of only the electric motor, and engine running mode relaying on another drive-power source mainly composed of the engine.
For instance, Patent Publication 1 (Japanese Patent Application Publication No. 2005-304201) discloses a hybrid vehicle having a control device of such a structure described above. Patent Publication 1 discloses a technology in which the drive-power source includes the engine and electric motor and an EV-running mode is continuously conducted under a situation where during a motor running mode (EV-running mode), a demanded torque command value is less than a given EV-drive permit reference value, whereas when the demanded torque command value exceeds the given EV-drive permit reference value, the engine is started up to carry out the engine running mode.
Besides the foregoing, various technologies have heretofore been known as disclosed in Patent Publication 2 (Japanese Patent Application Publication No. 2005-271618), Patent Publication 3 (Japanese Patent Application Publication No. 2006-180626), Patent Publication 4 (Japanese Patent Application Publication No. 2001-105932) and Patent Publication 5 (Japanese Patent Application Publication No. 2005-178626).
Meanwhile, under a circumstance where a vehicle is traveling on a road around a residential area or the like with a worrisome engine sound in concern, a strong demand conceivably occurs for the motor running mode to be continued for a time period as long as possible. However, if an accelerator pedal is depressed even on at least temporary basis, the demanded torque command value increases during the motor running mode. In this case, it is likely that engine startup occurs regardless of whether a strong or weak requirement is present for the motor running mode to be continued.